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SSA Disk Concurrent Mode of Operation Interface
The SSA subsystem provides support for the broadcast of one-byte message codes
from one using system to all other using systems that are connected to the same disk
drive. This ability to pass messages can be used to synchronize access to the disk
drive. The operating system has a concurrent mode interface to handle the sending and
receiving of messages.
The concurrent mode of operation requires that a top kernel extension run on all the
using systems that are sharing a disk drive. The top kernel extensions use the
concurrent mode interface of the SSA disk device driver to communicate with each
other through the SSA subsystem. The interface allows a top kernel extension to send
and receive messages between using systems.
The concurrent mode interface consists of an entry point in the SSA disk device driver
and an entry point in the top kernel extension. Two ioctls register and unregister the top
kernel extension with the SSA disk device driver. The SSA Disk Device Driver entry
point provides the method of sending messages, and of locking, unlocking, and testing
the disk drive. The top kernel extension entry point processes interrupts, which might
include the receiving of messages from other using systems.
Note: To ensure that the concurrent mode interface works, set the node_number
Device Driver Entry Point
The SSA disk device driver concurrent mode entry point sends commands from the top
kernel extension that is related to a specified SSA disk drive. The top kernel extension
calls this entry point directly. The DD_CONC_REGISTER ioctl operation registers entry
points.
This entry point function takes one argument that is defined in the
/usr/include/sys/ddconc.h file. The argument is a pointer to a conc_cmd structure.
The conc_cmd structures must be allocated by the top kernel extension. The
concurrent mode command operation is specified by the
structure. For each operation, the
appropriate SSA disk drive. The concurrent mode command operation can have the
following values:
DD_CONC_SEND_REFRESH
DD_CONC_LOCK
DD_CONC_UNLOCK
attribute of the ssar router (see "Reserving Disk Drives" on page 27) to a
different non-zero value for each using system that is sharing a disk drive.
Broadcasts the one-byte message code that is specified by the message field
of the conc_cmd structure. The code is sent to all using systems that are
connected to the SSA disk drive.
Locks the specified SSA disk drive for this using system only. No other using
systems can modify data that is on the disk drive.
Unlocks the SSA disk drive. Other using systems can lock and modify data
that is on the disk drive.
field in the conc_cmd
field of the conc_cmd structure specifies the
Chapter 13. Using the Programming Interface
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